Various types of combustion apparatus have been available for burning substances in a combustion furnace, such as boilers for burning fuel or refuse incinerators for burning garbage. For example, disclosed in Patent Literature 1 is a coal-fired boiler in which powdered coal is supplied to a combustion furnace along with air to burn the powdered coal within the combustion furnace, allowing the heat generated by combustion to heat a boiler tube and thereby generate steam within the boiler tube.